<h1><a href="https://material.io/design/components/text-fields.html">Material Design</a> like form input text fields with CSS only</h1>

<div class="container">
  <form novalidate>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <input id="firstname" type="text" class="form-field__input" placeholder=" " />
            <label for="firstname" class="form-field__label">First name</label>
            <div class="form-field__bar"></div>
          </div>
        </div>
      </div>
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <input id="lastname" type="text" class="form-field__input" placeholder=" " />
            <label for="lastname"class="form-field__label">Last name</label>
            <div class="form-field__bar"></div>
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <input id="email" type="email" class="form-field__input" placeholder=" " />
            <label for="email" class="form-field__label">Email</label>
            <div class="form-field__bar"></div>
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <input id="street" type="text" class="form-field__input" placeholder=" " />
            <label for="street"class="form-field__label">Street address</label>
            <div class="form-field__bar"></div>
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <input id="zip" type="text" class="form-field__input" placeholder=" " />
            <label for="zip"class="form-field__label">Zip code</label>
            <div class="form-field__bar"></div>
          </div>
        </div>
      </div>
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <input id="city" type="text" class="form-field__input" placeholder=" " />
            <label for="city"class="form-field__label">City</label>
            <div class="form-field__bar"></div>
          </div>
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-sm">
        <div class="form-field">
          <div class="form-field__control">
            <textarea id="additionalInfo" class="form-field__textarea" placeholder=" "></textarea>
            <label for="additionalInfo" class="form-field__label">Additional info</label>
            <div class="form-field__bar"></div>
          </div>
        </div>      
      </div>
    </div>
  </form>
</div>

<p style="text-align:center">Read more: <a href="https://auralinna.blog/post/2018/how-to-create-material-design-like-form-text-fields" target="_blank" rel="noopener noreferrer">How to create Material Design like form text fields with floating label and animated underline bar</a></p>

<p style="text-align:center">See also: <a href="https://codepen.io/teroauralinna/pen/rZZGpe" target="_blank">Javascript version</a></p>
html, body {
  color: #333;
  font-size: 16px;
  line-height: 20px;
}
body {
  margin: 20px;
}

h1 {
  line-height: 1.2;
  margin-bottom: 35px;
  text-align: center;
}

.container {
  margin: 0 auto 35px;
  max-width: 450px;
}

/* Actual code example */

$primary-color: #b11adc;
$animation-duration: 0.4s;

@mixin label-inactive() {
  font-size: 1.2rem;
  transform: translateY(0);
}

@mixin label-active() {
  font-size: 0.75rem;
  transform: translateY(-14px);
}

.form-field {
  display: block;
  margin-bottom: 16px;
}
.form-field__label {
  @include label-active();
  display: block;
  font-weight: normal;
  left: 0;
  margin: 0;
  padding: 18px 12px 0;
  position: absolute;
  top: 0;
  transition: all $animation-duration;
  width: 100%;
}
.form-field__control {
  background: #eee;
  border-radius: 8px 8px 0 0;
  overflow: hidden;
  position: relative;
  width: 100%;
}
.form-field__bar {
  border-bottom: 2px solid $primary-color;
  bottom: 0;
  content: "";
  display: block;
  left: 0;
  margin: 0 auto;
  position: absolute;
  right: 0;
  transform: scaleX(0);
  transition: all $animation-duration;
  width: 1%;
}
.form-field__input,
.form-field__textarea {
  appearance: none;
  background: transparent;
  border: 0;
  border-bottom: 1px solid #999;
  color: #333;
  display: block;
  font-size: 1.2rem;
  margin-top: 24px;
  outline: 0;
  padding: 0 12px 10px 12px;
  width: 100%;
  
  // IE 10-11
  &:-ms-input-placeholder {
    ~ .form-field__label {
      @include label-inactive();
    }
  }
  // All other browsers except Edge
  &:placeholder-shown {
    ~ .form-field__label {
      @include label-inactive();
    }
  }
  &:focus {
    ~ .form-field__label {
      color: $primary-color;
      @include label-active();
    }
    ~ .form-field__bar {
      border-bottom: 2px solid $primary-color;
      transform: scaleX(150);
    }
  }
}
.form-field__textarea {
  height: 150px;
}

External CSS

  1. https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap-reboot.min.css
  2. https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap-grid.min.css

External JavaScript

This Pen doesn't use any external JavaScript resources.